A topic that resurfaced in BBO forums last year http://forums.bridgebase.com/index.php?showtopic=16087 was the question about what to lead vs 3NT with 5-4; the longer or the shorter suit?
The question was first raised on a blog http://freebridge.blogspot.com/2006/08/what-lead-with-5-4-against-nt.html and I commented, referencing Paul Marston from a long time ago. Paul, I even talked to him in person about his hypothesis at one time, claimed that leading the shorter suit will collect more tricks.
As I recently found the original article from Australian Bridge (February 1986) I thought it would be interesting to re-visit this theme. Paul was playing with Stephen Burgess, a very successful partnership, at the time and this was a joint observation. The main reason why long suit leads work out badly is that partner is usually short in the suit. "This should be no surprise, because if the opponents have no good fit, nor do you."
"Ideally you would know when to take the risk associated with an attack and indeed it will often be clear that you must start aggressively by leading your long suit. The enemy bidding may have been very strong, or your cards may be lying very well for declarer and you will sometimes conclude that you muct pin all your hopes on your long suit lead striking blood. These clear situations, however, are not common so you will ususally have to fall back on general principles."
"The 4-card lead has a balance of aggression about it. It may be hitting at declarer's weakest point and, if it is, the declarer will be helpless. The defenders will have good communications since both probably hold four cards in the suit, rendering such standard techniques such as the hold-up play useless."
So what was his verdict on canapé leads back then? Paul analysed a 500 deal sample (notrump hands of about game strength where the leader had a 4-card suit and a longer side suit), the 4-card lead took more tricks overall (773 vs 746 on the 180 deals where the lead mattered) and the 5-card lead beat 3NT more often (52 vs 40).
A potential problem is that partner may not later realize that you have another longer suit that should be attacked upon gaining the lead.
I've used canapé leads to good effect many times, more than once regretted occasions when I didn't honor this advice. Paul concluded:
"Canapé leads are a winning style overall, but not on every single hand."
Further down the road:
Johan Bennet has done general simulations (back in ca 92/93) on whether you should attack or not with a 5-card suit after 1NT-3NT (disregarding presence of 4-card side suit). His finding was that with an ace somewhere (not necessarily in led suit), you should lead the 5-card suit, otherwise go passive. To summarize his findings: you need an entry.
I always keep these observations in mind. Maybe you should too.